Ga 1-x Al X As nanostructures grown on the gaAs surface by ion implantation

Materials and methods
The test items were d = 500 nm thick n- and p-GaAs(111) films. The films were bombarded with Al⁺ ions with ion energies E₀ ranging from 0.5 to 5.0 keV and irradiation dose D ranging from 10¹⁴ to 10¹⁷ cm^-2.
Scanning electron microscopy (SEM), high-energy electron diffraction (HEED), auger electron spectroscopy (AES), and UV photoelectron spectroscopy (UVPS) were used in the study. Furthermore, we calculated the energy dependencies of the secondary electron emission coefficient (SEEC). Layer-by-layer Auger analysis was used to get the atom depth profile. To do this, the sample's surface was sputtered (etched) by 3-keV Ar⁺ ions incident at an angle of roughly 85° to the normal. The etch rate was changed within a range of (5 1)/min. UV photoelectron spectra were collected at photon energies of hv 10.8 eV. As a UV photon source, a typical gas-discharge hydrogen lamp was used. A SUPRA-40 device was used to take SEM micrographs. See [11] for further information on the experimental procedure.
Result and Discussion
SEM micrographs and HEED patterns (insets) of the as-grown GaAs(111) surface and Ga_1-xAl_xAs films generated by heating to 850 K following implantation of Al⁺ ions with E₀ = 1 keV and D = 4×10¹⁶ cm^-2 are shown in Figure 1. In the present example, Auger data show that x falls between the range of 0.45-0.50. As a result, the approximate composition of the resultant chemical is Ga_0.5Al_0.5As. The quantity of Al can be reduced by raising the temperature. For example, the surface concentration of Al at 950 K was 15-20 at%, and the film's composition was Ga_0.7Al_0.3As. According to Fig. 1, the GaAs surface exhibits a flat microrelief. The Ga_0.5Al_0.5As nanofilm is made up of singlecrystalline nanoblocks with surface sizes d = 10-20 nm. Despite the fact that these blocks were produced epitaxially, the grain-boundary crystallographic orientations of several of them varied. As a result, concentric rings of individual diffraction spots, typical of textured films, show in the HEED patterns. We found that when ion-implanted GaAs is annealed by laser radiation with energy density W = 1.6 J/cm² and then is rapidly heated to 900–950 K, a homogeneous epitaxial Ga0.5Al0.5As film grows on the GaAs surface. The atom distribution profile taken of this system suggests that the Ga0.5Al0.5As film is 3.5– 4.0 nm thick, and the thickness of the transition layer, where the Al concentration monotonically drops from 25 at % to zero, equals 5–6 nm (Fig. 2).

Fig. 1. SEM micrographs and HEED patterns of the surface of (a) GaAs(111) and (b) Ga0.5Al0.5As films formed by 1-keV Al^+ ion implantation with a dosage of 4×1016 cm^-2 followed by heating are shown

The photoelectron spectra of GaAs and the Ga_0.5Al_0.5As film were recorded at photon energy of 10.8 keV in Figure 3. Four different peaks can be detected in the spectrum of GaAs, which are caused by the excitation of s-electrons in As and p-electrons in Ga and As. Additionally, surface state-related singularities are seen close to E₄ as well. The following modifications occur because of ternary compound production.
(i) Peak EV moves 0.3–0.4 eV farther from EB as the spectrum grows 0.3–0.4 eV narrower.
(ii) Peak E1 broadens significantly and transitions toward higher energies. We believe that this peak was formed in part by the 4p-electrons of Ga and the 3p-electrons of Al.
(iii) The magnitude of the Peak E2 caused by the splitting of the p-states in Ga, Al, and As moves to the right by 0.1–0.2 eV.

Fig. 2. The Ga0.5Al0.5As /GaAs system's depth profile was created via the implantation of 1-keV Al^+ ions with a dosage of 4×1016 cm^-2 into GaAs, followed by (laser + thermal) annealing.

(iv) The only significant difference between the arsenic peaks E₃ and E₄ is a little shift in their intensities.
Ga_0.5Al_0.5As films with thicknesses between 2.0-2.5 and 6.0-7.0 nm may be grown by varying the energy of Al ions in the range of 0.5-5.0 keV. GaAs implanted with Al ions at energy E₀ = 1 keV and low dose (D = 8×10¹⁴ cm^-2) underwent (laser + thermal) annealing to form epitaxial nanocrystalline phases of the ternary Ga_0.5Al_0.5As compound, which, like Si [12], had surface diameter d = 15-20 nm. These phases' centers were separated by 50–60 nm. It is well known that the band diagrams of semiconductors and dielectrics coincide with the energy dependence of the SEEC measured in the energy range of 1–25 eV [13]. The (Ep), R(Ep), and (Ep) curves for the Ga_0.5Al_0.5As /GaAs (111) nanofilms with thickness = 4 nm are shown in Figure 4. Here, R is the coefficient of elastically scattered electrons, is the total SEEC, is the coefficient of genuine secondary electrons, and is the total SEEC.

Fig. 3. Photoelectron spectra of three different films were obtained: (1) pure GaAs/Ge(111) film; (2) Ga0.5Al0.5As /GaAs(111) nanofilm; and (3) GaAs film containing Ga0.5Al0.5As nanocrystals that were 15-20 nm thick.

Figure 4 shows that the initial drop R is located between 2.0 and 2.1 eV. This decrease denotes the beginning of the inelastic scattering of electrons without their escape into the vacuum; in other words, electrons go from the top of the valence band to the bottom of the conduction band, or = E_g. When begins to increase, R experiences its second abrupt dip. Here, electron emission into a vacuum occurs, and the equation is Eg+χ.

Fig. 4. (Ep), R(Ep), as well as (Ep) profiles for the 4 nm thicker Ga0.5Al0.5As film

Thus, ion implantation combined with annealing is an effective way of producing ternary Ga_1−xAl_xAs nanofilms and nanocrystals in the surface area GaAs with new electronic properties.